For many years combines have been used in harvesting grain crops such as wheat, oats, barley and rye. A combine has means for cutting the grain and thereupon thrashing it to separate the grain kernels from the straw and chaff. The straw and chaff are usually scattered back onto the field while the grain is bagged, stored in a container or delivered into a truck which is driven alongside the combine.
By reason of the multiple functions it performs, a combine is a large and expensive piece of equipment. While in some cases a combine is pulled by a tractor, it is frequently self-propelled with the result that the weight and cost of the combine is further increased.